A router that is used to connect autonomous systems in a large internetwork such as the Internet.
Autonomous systems are large portions of an internetwork that fall under the administration of a single authority. In an autonomous system, routers exchange information with each other using routing protocols called Interior Gateway Protocols (IGPs), such as the Routing Information Protocol (RIP) and the Open Shortest Path First (OSPF) Protocol.
Backbone routers are then used to connect the various autonomous systems into a single internetwork. Backbone routers also exchange information using Exterior Gateway Protocols (EGPs), such as the Border Gateway Protocol (BGP).
Backbone routers must have high performance and reliability because they are typically used to aggregate and route traffic from dozens or hundreds of physical local area network (LAN) segments and to maintain routing information for thousands of machines.
Backbone routers can cost from $10,000 to $100,000 each, or more. They come with dedicated operating systems, such as Cisco Systems’ Internetwork Operating System (IOS).